Surgical filaments such as sutures and ligatures have been made from a variety of different materials. Some of these are degraded in the tissue after a certain period. Others remain unchanged. Polypropylene sutures are preferred by the medical profession on account of their extreme inertness. The properties can be summarized as follows:
a. they resist breakdown and do not promote infection; PA1 b. they maintain their in vivo tensile strength over extended periods; PA1 c. they show minimal reaction with body tissue; PA1 d. they have high tensile strength; PA1 e. they pass easily through body tissue; and PA1 f. they have good knot security.
The preferred polypropylene suture used in the medical profession today is described by Listner in U.S. Pat. No. 3,630,205.
The suture described by Listner has the following properties:
______________________________________ Tensile Strength 3.9-8.9 g/den about 320-730 N/mm.sup.2 Knot Strength 3.3-7.9 g/den about 270-650 N/mm.sup.2 Break Elongation 36-62% Young's Modulus 2200-3680 N/mm.sup.2 ______________________________________
As good as the current polypropylene sutures are, there is some room for improvement. In particular, it would be desirable to increase the compliance, limpness, or flexibility of polypropylene sutures in order to make them easier to tie and to improve their knot security. The problem is that previous efforts to accomplish this have occasioned a concomitant undesirable decrease in strength properties.